Method for isolating ultrafine and fine particles and resulting particles

ABSTRACT

A method of making isolated particles including the step of at least substantially encapsulating particles present in a highly dispersed colloidal suspension with an encapsulant material, such that the encapsulated particles remain independent and discrete upon separation from the suspension. Also, independent and discrete particles at least substantially encapsulated with the encapsulant material.

This is a continuation of application Ser. No. 08/962,652, filed Nov. 3,1997 now U.S. Pat. No. 6,190,731, which is a division of applicationSer. No. 08/614,020, filed Mar. 12, 1996, now U.S. Pat. No. 5,922,403.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to ultrafine and fine particles andmethods for making and isolating such particles.

2. Discussion of the Related Art

Ultrafine particles are defined in the art as having diameters of about100 nm or less. Such particles are therefore smaller than conventionalpowders, but larger than typical atom clusters. Ultrafine particles areof great interest due to their numerous applications, including use inthe formation of ceramic and metal structures, conductive paths and/orconductive layers in electronic devices and the production of catalysts.For example, the use of ultrafine particles in forming ceramic and metalparts results in small grain size., thus providing the parts withoptimal physical properties (e.g., strength and ductility). Also, inelectronic devices, the small particles allow creation of finerconductor paths. Variations in processes used to produce ultrafineparticles may also produce larger, so-called “fine” particles, which aredefined as particles having diameters greater than 100 nm but less than1500 nm. For many of the applications in which ultrafine particles aredesired, fine particles may be equally useful.

It has been difficult, however, to obtain powder of ultrafine and fineparticles without experiencing agglomeration into larger, less usefulparticles. Thus, those skilled in the art have attempted to isolateultrafine and fine particles in a liquid suspension to prevent suchagglomeration.

For example, U.S. Pat. No. 4,872,905 discusses a method of obtainingparticles by utilizing a sputtering process and a liquid substrate. Themetal particles generated from the target electrode encounter vapors ofa heated liquid oil, are covered by the oil vapors, and are thencaptured by the liquid oil. A complex recovery process is required toobtain a usable end product. In particular, the liquid must be mixedwith two solvents, such as kerosene and acetone, to thin out the oil andform a colloidal suspension. The acetone (or comparable solvent having aboiling point lower than both the other solvent and the oil) is removedby heating the solution, and the oil-covered particles then settle inthe solution. This separation process may have to be performed up tofour times. Moreover, prior to using the particles, the oil coveringmust be removed, for example by washing the particles in a solvent suchas dioxane. Once the oil is dissolved, the particles will tend toagglomerate. Thus, while the method of this patent may offer a way ofstoring ultrafine or fine particles without agglomeration, it does notprovide a means for producing isolated particles in a state thatfacilitates the actual use of the particles.

Another patent dealing with ultrafine and fine particles, U.S. Pat. No.4,877,647, describes a method for obtaining a colloidal suspension ofmetal particles. Vaporized metal in a vacuum is captured by a solvent,which may be present as a gas or liquid. Typically, an external coolingset-up is provided, by which the solvent containing the captured metalatoms and atom clusters can be frozen to the interior of thevaporization vessel. The frozen matrix is slowly heated in the vessel toform a colloidal suspension of metal particles in the solvent. A largeexcess of solvent is required to obtain the suspension, however, atleast 30 to 1000 parts by weight of solvent. Preferred metal loadingsrange from 0.02 to 0.09 molar. Above this level, the metal particleswill tend to agglomerate and precipitate. Thus, ultrafine and fineparticles produced according to U.S. Pat. No. 4,877,647 are difficult toutilize in many applications, because they cannot be used separately anddistinctly from the large amount of solvent required. Moreover,reduction of the amount of solvent results in undesirable agglomeration,thereby destroying the particles usefulness.

The need therefore exists for methods of producing ultrafine and fineparticles that remain isolated from one another, yet are in a state thatfacilitates handling and maximizes potential applications.

SUMMARY OF THE INVENTION

The present invention is directed to a method for isolating particles.The method involves the step of at least substantially encapsulatingparticles present as a highly dispersed colloidal suspension with anencapsulant material, such that the encapsulated particles remainindependent and discrete upon separation from the suspension.

The present invention is also directed to a method for isolatingultrafine particles, including the steps of preparing a highly dispersedcolloidal suspension of ultrafine particles of at least one metal in anorganic solvent, adding to the suspension an encapsulant material suchthat the ultrafine particles are substantially encapsulated by theencapsulant material, and separating the encapsulated particles from thesuspension.

The present invention is further directed to independent and discreteultrafine and fine particles at least substantially encapsulated with anencapsulant material, wherein the encapsulant material is at least onecompound selected from an amine, an ether, a thiol, a sulfide, acarboxylic acid, a hydroxy acid, a sulfonic acid, a polyhydroxy alcohol,an organosilane, a titanate, a zirconate, a zircoaluminate, acarboxylate, a sulfate, a sulfonate, an ammonium salt, a pyrrole, afuran, a thiophene, an imidazole, an oxazole, a thiazole, a pyrazole, apyrroline, a pyrrolidine, a pyridine, a pyrimidine, a purine, atriazole, a triazine, and derivatives thereof, such that the particlesremain independent and distinct.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

DETAILED DESCRIPTION OF THE INVENTION

The method of the present invention is applicable to particles of metalelements, nonmetal elements, inorganic compounds, and organic compounds,these particles capable of forming a highly dispersed colloidalsuspension.

Solid elements such as boron, carbon, silicon and the Main Group metals,such as aluminum, beryllium, magnesium, etc., which are capable offorming atomic and cluster species in the gas phase, can form particlesin a controlled fashion in a suitable medium to form colloidalsuspensions.

Inorganic solid compounds, such as metal oxides, sulfides, selenides,tellurides, phosphides, antimonides, fluorides and other halidederivatives are known to form colloidal particles in suitable medium.Similarly, other inorganic compounds such as borides, carbides, nitridesand suicides form ultrafine: a particles in a controlled manner. Binary,ternary, and quaternary metal alloys, and the like, and intermetalliccompounds can also form ultrafine particles using appropriate methodsand conditions. Both organic and inorganic pigments, which may beproduced by a variety of methods, require a great deal of physical andinnovative effort to keep them well dispersed in a medium and producethem in a desired particle size and size distribution. The ability tokeep such materials as discrete particles therefore enhances theefficiency of their production methods and improves their functionalproperties.

The initial step in producing isolated metal particles according to oneembodiment of the present invention is formation of a highly dispersedcolloidal suspension of metal particles in an organic solvent. One wayto prepare such a suspension is described in U.S. Pat. No. 4,877,647,the entire disclosure of which is incorporated by reference herein.

The suspension may be prepared by first vaporizing a metal or metals toobtain metal atoms and atom clusters. The metal or metals preferablyhave an atomic number from 21 to 32, 39 to 50 and/or 72 to 82. The metalatoms and atom clusters are captured in a vaporized state in an organicsolvent vapor. The atom- and atom cluster-containing solvent vapor isfrozen or substantially frozen to form a matrix. The matrix is graduallywarmed to room temperature without precipitating the captured metalatoms and atom clusters.

While all the metals listed above may be used, preferred metals forforming ultrafine particles are cobalt, nickel, copper, palladium,silver, platinum, gold, tin, lead, and mixtures thereof.

In such a method, the metal or metals are preferably evaporated under avacuum with the resultant metal atoms and atom clusters condensedsimultaneously with an organic solvent in vapor or liquid form toproduce a frozen or substantially frozen matrix. A vacuum below 10⁻²torr, preferably below 10 ⁻⁴ torr, may be employed. Because an extremelycold surface is necessary to condense and freeze the metal atoms andmetal clusters and the solvent to form a solid matrix, liquid nitrogencooling may be used to freeze the matrix onto the interior of theevacuated chamber. It is preferred that the matrix of the metal atomsand atom clusters and solvent vapors be completely frozen, because aprocess involving a frozen or solid matrix is easier to control and willproduce better results than a process involving a partially frozenmatrix.

The solid matrix is preferably allowed to warm up slowly to roomtemperature, e.g., in a time period from one to four hours, to obtainthe suspension. Alternatively, additional solvent that has been cooledto within about 15° C. of its freezing point may be added to the frozenmatrix, or the frozen matrix may be transferred to a vessel containingsimilarly cooled solvent. During such a transfer of the frozen matrix,or addition of solvent, it is preferable to keep the solvent vigorouslyagitated. This agitation speeds up the warming of the frozen matrix andhelps to control the atom clustering process, thereby allowingattainment of particles of the desired size. This agitation alsominimizes the amount of solvent required.

A preferred apparatus for preparing the suspension includes a rotary orstatic reactor assembly connected to a vacuum pump. The reactor assemblymay consist of a flask equipped with a resistance heating source tovaporize the metal or metals being used. An electron gun, or the like,may be used instead of a resistance heating source. In addition, thereactor assembly may be equipped with one or more vaporizing sources. Aninlet may be provided to introduce the solvent into the flask,preferably directing the solvent toward the flask walls to promoteformation of the matrix. An external cooling set-up is preferablyprovided to condense and freeze the evaporated metal and the solvent onthe flask walls.

At extremely low loadings of metal in the solvent, the metal is presentas zero-valent solvated atoms or small atom clusters. The salvationphenomenon is characterized by a strong interaction between the atoms oratom clusters with the solvent, resulting in the shifting of electronsfrom the metal to the solvent molecules or vice versa. This shifting ofelectrons creates localized charges which provide charge stabilizationto the suspension.

At higher loadings, the short-lived solvated metal atoms or atomclusters seek thermodynamic equilibrium by forming larger clusters, thusminimizing the free energy of interfaces. This leads to the formation ofultrafine or fine particles, depending on the amount of clustering. Thisphenomenon is highly controllable with the proper selection ofmetal-solvent combinations, solvent flow rate, concentration,temperature, and evaporation rate of the metal. Selection of thesevariables will optimally result in the formation of particles of thedesired size. Particles produced by this method exist as highlydispersed colloidal suspensions characterized by high stability. A“stable” colloidal suspension is defined as a dispersion of colloidalparticles that remain evenly distributed throughout the medium forseveral days, weeks or months without settling, agglomeration, or anychange in the size of the discrete particles. The solvent prevents themetal particles from interacting or associating with each other, and forsome solvent-metal pairs the suspension may remain stable indefinitelyat ambient conditions.

The term “solvent” as used herein encompasses organic liquids which arecommonly referred to in the art as solvents, and which are able to formthe colloidal suspensions discussed above. Polar organic solvents arepreferred due to their greater ability to complex or solvate metal atomsand ago clusters in comparison to non-polar solvents, but any solventwhich forms the desired colloidal suspension is suitable. Preferreddielectric constants for the solvent range from about 10 to about 55.Suitable solvents include ketones, alcohols, ethers and the like.Examples include, but are not limited to, acetone, methyl ethyl ketone,ethanol, propanol, dimethylformamide, triethylamine, benzaldehyde,acetaldehyde, tetrahydrofuran, dimethyl sulfoxide, and the like.Preferred solvents are acetone, tetrahydrofuran, methanol, ethanol,1-propanol, 2-propanol, and the like. In the case of metal atoms, thesolvent should be substantially non-reactive with the atoms at theconditions of the condensation in the reactor chamber, i.e., within 25°C. of the solvent's freezing point.

Similar methods for producing a colloidal suspension of metal particlesin a solvent from vaporized atoms and atom clusters of metal are equallysuitable for use in the present invention, as are all methods of formingsuspensions of particles of non-metal elements, organic compounds, andinorganic compounds. Examples of such suspensions include, but are notlimited to, hydrosols, organosols, and aerosols.

Common to all such methods of forming colloidal suspensions, however, isthe need for a large excess of solvent, particularly in hydrosol andorganosol systems, relative to the amount of recoverable and usableparticles. The large amount of solvent required is problematic, in thatit limits the usefulness of the particles for practical applications.

According to the present invention, an encapsulant material is added toa highly dispersed colloidal suspension of particles and substantiallyencapsulates the particles by forming an ionic or covalent bond with theparticles, or by adsorbing onto the particles' surfaces. The term“encapsulate,” as used herein, means the thermodynamically drivenprocess in which the molecules of the encapsulant material coat or coverthe particles, i.e., the molecules of encapsulant material at leastpartially cover the particles or take the form of a monolayer coating orsheath around the particles. Preferably, the entire surface of aparticle is encapsulated. Optimally, the coating effectively preventsdirect particle-particle interaction, thus preventing agglomeration ofthe particles. Instances of (a) adsorption of a single molecule ofencapsulant material by two or more particles, and (b) weak interactionbetween adsorbed encapsulant material on separate particles, result in aweak connection between a majority of the encapsulated particles. Theresulting interaction creates an open three dimensional network, and, asthe networks of encapsulated particles grow, the networked particlesbegin to flocculate. The particles, however, due to the encapsulation,remain independent and discrete throughout this flocculating process.Preferably, the flocculent settles out of the suspension, thereby easingthe recovery of the material. After settling out of the suspension, thematerial is easily re-dispersed by simple agitation. Upon separationfrom the suspension, the particles remain encapsulated as discreteentities at ambient conditions, but become available in a moreconcentrated and useful form.

The encapsulant material may be one or more compounds selected from anamine, an ether, a thiol, a sulfide, a carboxylic acid, a hydroxy acid,a sulfonic acid, a polyhydroxy alcohol, an organosilane, a titanate, azirconate, a zircoaluminate, a carboxylate, a sulfate, a sulfonate, anammonium salt, a pyrrole, a furan, a thiophene, an imidazole, anoxazole, a thiazole, a pyrazole, a pyrroline, a pyrrolidine, a pyridine,a pyrimidine, a purine, a triazole, a triazine, and derivatives of anyof these compounds. Of these materials, an amine, an ether, a thiol, asulfide, a carboxylic acid, a hydroxy acid, a sulfonic acid, apolyhydroxy alcohol, or derivatives thereof are preferred for metalparticles; an organosilane, a titanate, a zirconate, a zircoaluminate, acarboxylate, a sulfate, a sulfonate, an ammonium salt, or derivativesthereof are preferred for non-metal particles; and a pyrrole, a furan, athiophene, an imidazole, an oxazole, a thiazole, a pyrazole, apyrroline, a pyrrolidine, a pyridine, a pyrimidine, a purine, atriazole, a triazine, or derivatives thereof are suitable for metals andsome non-metals, but are preferred for metals. An appropriateencapsulant material may be chosen by one skilled in the art based onthe characteristics of the particles and solvent.

Preferred encapsulant materials for metal particles are one or morecompounds selected from triethanol amine, ethylenediamine, oleic acid,malonic acid, hydroxyacetic acid, dimethyl sulfoxide, propylene glycol,hexanetriol, dioxane, diethylene glycol dimethyl ether,dimethylformamide, 1-(2-cyanoethyl)pyrrole, 3-(2-furyl)acrylonitrile,3-thiophenemalonic acid, mercaptobenzimidazole, 2-mercaptobenzoxazole,6-aminobenzothiazole, 3-(2-aminoethyl)pyrazole,1-pyrrolidinebutyronitrile, 3-pyridineacrylic acid,4,6-dihydroxypyrimidine, 6-mercaptopurine, 1-chlorobenzotriazole,2,4,6-triallyloxy-1,3,5-triazine, and derivatives thereof. Particularlypreferred compounds for metal particles are malonic acid, oleic acid,1,2,6-hexanetriol, and triethanolamine.

Monolayer forming compounds known as self-assembled monolayers, such asalkanethiols, dialkyl sulfides, dialkyl disulfides, alcohols, amines,and carboxylic acids are useful encapsulant materials for both metal andnon-metal particles. Preferred compounds of this group are undecanethioland diundecyl disulfide.

Encapsulants for non-metal particles with hydroxylated surfaces, such assilica, silicon, alumina, and the like, include coupling agents such asorganosilanes, titanates, zirconates, and zircoaluminates. Preferredencapsulants of this type are trimethylethoxysilane,isopropyltriisostearoyltitanate, and neoalkoxytrisneodecanoylzirconate.

Encapsulants of the amphipathic type, for example, surface active agentssuch as carboxylates, sulfates, sulfonates, and ammonium salts are alsouseful encapsulant materials for non-metals. Preferred amphipathic typeencapsulant materials are sodium stearate, sodium cetyl sulfate, sodiumdiisopropylnapthalene sulfonate, and cetyltrimethylammonium bromide.

The encapsulant material may be mixed with a solvent prior to adding theencapsulant material to the suspension, or, similarly, the encapsulantmaterial can be added to the suspension along with additional solvent.

The amount of the encapsulant material to be added to a certainsuspension may be determined by “titrations” of about 4 to 8 aliquotsamples of the suspension. To each sample of the suspension, aprogressively increasing amount of the encapsulant material, eitheralone or in solution, is preferably added. After 1 to 6 hours, twolayers are formed—a first “sediment” layer containing the isolatedencapsulated particles and a second layer ranging from clear to a colornear that of the starting suspension. The sample having a clear secondlayer, yet with the smallest amount of added encapsulant material, isused to determine how much encapsulant material should be added to thesuspension. Theoretically, this amount is the minimum amount needed toprovide complete surface coverage to all the particles in thesuspension. The actual amount required further depends on the totalsurface area of all the particles present in the suspension and thenature of interaction between the particles and the encapsulant. In someaerosol systems, in situ encapsulation may be difficult to control andmay not be fully effective in producing and maintaining discreteparticles.

The flocculent containing the isolated encapsulated particles can beseparated from the solvent of the suspension by any conventional means,such as decanting the clear solvent layer or separating the lower layercontaining the particles using a separatory funnel or similar apparatus.The recovered particles retain the encapsulation, along with a smallamount of excess encapsulant material and residual solvent. Therecovered particles thus take the form of an “ink.” This “ink”constitutes a concentrated, more useful form of ultrafine or fineparticles, wherein the individual particles remain independent anddiscrete. In this “ink” form, the particles remain isolated indefinitelyat ambient conditions in sealed containers and may also be handled inthe open air. The amount of excess encapsulant material and solvent inthe “ink” can be reduced by allowing the solvent to evaporate by blowingwith a stream of nitrogen gas, or by other means known in the art.

In addition to providing a more concentrated and useful form of isolatedultrafine particles, the present invention also results in particleshaving a narrow particle size distribution. This is due to thecontrolled atom clustering and nucleation process involved, as well asthe phenomenon wherein the solvated metal atoms or atom clusters seekthermodynamic equilibrium by forming larger clusters to minimize thefree energy of interfaces. Stability is also imparted by theencapsulation, which minimizes particle-particle interaction, and thusagglomeration. Typically, ultrafine particles formed according to thepresent invention will have an average diameter ranging from 20 nm to 70nm, depending on the particular metal or metals used and the conditionsemployed. Larger, “fine” particles produced by adjustment of the processconditions will typically have diameters ranging from 100 nm to 1500 nm.

The concentrated, encapsulated, and isolated particles made according tothe present invention may be used for a variety of applications. Whenusing the particles for coating a substrate, additives such as fluxingagents, as well as a variety of surface treatment techniques, mayprovide enhanced adherence of the coating to the substrate. Suitablesubstrates include ceramics, metals, glass, polymer films, and variousfibers. The particle “ink” may also be used for metal joiningapplications such as electronic component attachment. When the “ink” isapplied in coatings or metal joining, under conventional coating ormetal joining conditions, the encapsulant will typically evaporate fromthe particles or will form a liquid that can be washed off, leaving theultrafine particles to interact and form a continuous layer or coating.Also, fibers such as, for example, Kevlar®, Nylon®, and natural fibersmay be dipped into a metal particle “ink” of the present invention toimpart conductivity. In addition a metal particle “ink” may be used toform solder paste and solder ink, or other metal inks. Metal particlesof the invention may also be used to obtain a desired grain structure inceramics, metals, and metal/ceramic composites. Specifically,manipulation of forming and treating conditions, within the knowledge ofone skilled in the art, can be used to obtain a variety of grainstructures to optimize properties such as strength and ductility. Otheruses will be apparent to those skilled in the art.

The invention will be further clarified by the following examples, whichare intended to be purely exemplary of the invention. In the examplesbelow, all parts and percentages are by weight unless otherwiseindicated. The solvents, except the alcohols, were dried with lithiumaluminum hydride (e.g., Baker P403-05). Alcohols with low water contentwere dried over lithium hydride (Aldrich 20, 104-9). Solvents suspectedof containing peroxides such as tetrahydrofuran were first treated withcuprous chloride to remove the peroxide and then dried with lithiumaluminum hydride. After drying, the solvents were vacuum distilled andthoroughly degassed and were stored in special solvent vessels.

EXAMPLE 1

Preparation of Metal Particle Suspensions

A reactor assembly consisting of a 3-liter cylindrical heavy-wallreaction flask and a flask head having five openings, with extra-thickfinely ground flat flanges, was securely held together with a clamp. Theflask was connected to a vacuum system through the middle joint of thethree in-line ground glass joints. One ground joint was used to connecta product vessel having a Teflon® needle valve with a capillary rodwhich was used to recover the colloidal suspension from the bottom ofthe flask, and the third ground joint was sealed with a penny-headjoint. The remaining two openings, one on each side of the ground jointswere fitted with o-ring joints. Two electrodes were inserted throughthese openings and a resistively heated alumina coated tungsten crucible(Sylvania GTE Emissive Products 038314) was attached to the electrodes.

The system, after loading the crucible with the metal to be evaporated,was evacuated until a 1.0×10⁻⁶ torr reading was obtained with an iongauge. The flask was then immersed in a Dewar containing liquidnitrogen. The reactor and the main manifold was isolated and the solventvessel opened to transfer solvent in the vapor phase to the reactor.After sufficient solvent had deposited on the walls of the reactor, thecrucible was heated to evaporate the metal at a controllable rate, suchthat there was adequate solvent matrix for the metal vapor. The metalvapor made up of metal atoms and small atom clusters was captured in thematrix in this form. After enough metal was evaporated, the reactor wasisolated and the frozen matrix allowed to slowly warm up by allowing theliquid nitrogen in the Dewar to evaporate over approximately two hours.During the warm up, particles began to form from the atoms and atomclusters, and the resultant product was a stable, highly dispersed,colloidal suspension. The suspension was transferred through thecapillary rod to the product vessel, which had been evacuated with thereactor and was kept isolated at 1.0×10⁻⁶ torr during the vaporizationof the metal. Before the needle valve was opened, the reactor was filledwith dry argon (0.5 ppm of water and less than 0.2 ppm of oxygen).

A series of experiments using lead, tin, and copper metals intetrahydrofuran solvents were performed. Particle size measurement wasperformed using a Malvern 4700 V4 particle size analyzer by photoncorrelation spectroscopy. The results of these experiments aresummarized in Table 1.

TABLE 1 Run Metal Solvent Particle Size (nm) 1 lead tetrahydrofuran 1222 ″ ″ 111 3 ″ ″ 108 4 ″ ″ 276 5 ″ ″ 491 6 ″ ″ 546 7 ″ ″ 193 8 ″ ″ 186 9″ ″ 53 10 ″ ″ 61 11 ″ ″ 76 12 tin tetrahydrofuran 125 13 ″ ″ 63 14 ″ ″56 15 ″ ″ 23 16 ″ ″ 53 17 ″ ″ 25 18 ″ ″ 17 19 copper tetrahydrofuran 22320 ″ ″ 254 21 ″ ″ 108 22 ″ ″ 98 23 ″ ″ 111 24 ″ ″ 236

By changing the vaporization rate of the metal and keeping the flow rateof the solvent constant, the particle size of the suspension can becontrolled. The slightest exposure to even adsorbed water in glasswareor trace amounts of oxygen was found to destabilize the suspension.

EXAMPLE 2

Preparation of Metal Particle Suspensions

Again using a rotary reactor, the effect of metal loading in isopropanolsolvent for copper, tin, and lead was examined. In addition, particlesof a tin-lead alloy were produced by alternating the vaporization of thetwo metals from different crucibles. The results are shown in Table 2

TABLE 2 Metal Loading Particle Size Run # Metal (mg/mL) (nm) 1 copper6.40 464 2 copper 4.10 77 3 tin 6.68 62 4 tin 1.69 712 5 lead 0.44 125 6lead 1.93 221 7 copper 21.75 252 8 tin-lead 2.76/1.56 68

EXAMPLES 3, 4 and 5

Preparation of Isolated Particles

The following colloidal suspensions of tin, lead and tin/lead alloy wereprepared (suspensions A, B, and C, pespectively), along with a solutionof malonic acid in triethanolamine (solution D).

A. Tin particle suspension in isopropanol having particle size of 62 nm.

B. Lead particle suspension in isopropanol having particle size of 221nm.

C. Tin/lead alloy particle suspension in isopropanol having particlesize of 68 nm.

D. In a beaker, 300.00 g of triethanolamine (J. T. Baker 9468-01) and60.00 g of malonic acid (Aldrich M129-6) were mixed with a Cowles bladefor 4 hours at 85 -90° C. to dissolve the malonic acid intriethanolamine, thus forming an encapsulant material.

EXAMPLE 3

Six test tubes were transferred into an argon filled dry box (0.5 ppm ofwater and less than 0.2 ppm of oxygen) and contained the followingsuspensions and solutions.

A-1. 0.0315 g of solution D in 0.75 mL of isopropanol. (encapsulantmaterial)

B-1. 0.0310 g of solution D in 0.75 mL of isopropanol. (encapsulantmaterial)

C-1. 0.0330 g of triethanolamine in 0.75 mL of isopropanol. (encapsulantmaterial)

D-1. 0.0322 g of triethanolamine in 0.75 mL of isopropanol. (encapsulantmaterial)

E-1. 0.0074 g of malonic acid in 0.75 mL of isopropanol. (encapsulantmaterial)

F-1. 0.0071 g of malonic acid in 0.75 mL of isopropanol. (encapsulantmaterial)

In three culture tubes, the following samples were prepared by mixingamounts from the above samples:

A-2. To 5.0 mL of suspension C was added encapsulant material C-1.

B-2. To 5.0 mL of suspension C was added encapsulant material E-1.

C-2. To 5.0 mL of suspension C was added 50 μL of oleic acid in 750 μLof isopropanol.

The contents of samples A-2, B-2, and C-2 were mixed thoroughly byshaking the capped culture tubes. The suspensions became cloudier. Thedegree of cloudiness was: A-2>B-2>C-2. This indicated thattriethanolamine has a greater ability to encapsulate and flocculate theparticles in suspension than malonic acid, and that malonic acid has agreater ability to encapsulate and flocculate than oleic acid.

In an identical manner, when the contents of A-1, D-1, and F-1 wereadded to 5.00 mL of suspension C, the sample containing D-1 formedlarger particles which eventually became large clumps, while the othersamples become cloudy. Although A-1 contained triethanolamine along withmalonic acid, the amount of triethanolamine was critical inencapsulating the particles. These results suggested that the amount ofencapsulant material to be added should be determined by titratingaliquot samples.

EXAMPLE 4

The following encapsulant solutions were prepared in a argon-filled drybox.

A-3. 6.8 mg of malonic acid in 0.75 mL of isopropanol

B-3. 30 μL of oleic acid in 0.75 mL of isopropanol

C-3. 35.0 mg of triethanolamine in 0.75 mL of isopropanol

D-3. 30 μL of 1,2,6-hexanetriol (distilled and degassed) in 0.75 mL ofisopropanol

2.00 mL of suspension C was transferred into each of 5 smallpolyethylene bulbs. To four of the polyethylene bulbs 300 μL of solutionof A-3, B-3, C-3 and D-3 was added at a rate of 20 μL at intervals of1.5 seconds while the suspension was stirred using a magnetic stirrerand Teflone stir bar. The fifth polyethylene bulb was used as a control.

One drop was taken from each of the five bulbs, added to 2.00 mL ofisopropanol in particle size analysis test tubes, and the resultantsolution mixed well to prepare for particle size analysis to determinethe effect of adding the encapsulant to the suspension. The results arepresented in Table 3.

The interaction between encapsulated particles caused bridgingflocculation, i.e., flocculation of more than one encapsulated particle,which resulted in an apparent particle size larger than the controlsample. Thus, the measured particle size was actually the average sizeof flocculated particles (flocs). This was reflected by the fact thatthe apparent large sizes are multiples of the particle size obtained forthe control. The multimodal distribution in these samples also providedfurther confirmation of this conclusion. Both 1,2,6-hexanetriol andoleic acid were shown to be good encapsulants but relatively weakflocculating agents. Malonic acid and triethanolamine were shown to begood encapsulants as well as strong flocculants.

TABLE 3 Samples Particle Size (nm) Control 68 D-3 encapsulant 67 B-3encapsulant 68 A-3 encapsulant 129 C-3 encapsulant 680

EXAMPLE 5

In a 250 mL plastic beaker, 118 mL of suspension A and 58 mL ofsuspension B were combined in an argon-filled dry box. The suspensionwas mixed using a Teflone stir bar and magnetic stirrer. Approximately 5mL of this suspension was withdrawn to dissolve 1.2 mL of1,2,6-hexanetriol (distilled, degassed) (encapsulant material) and thesolution was returned to the beaker.

A solution was prepared by dissolving 0.50 mL of encapsulant material Din 7.50 mL of isopropanol. After the contents of the 250 mL beaker abovehad been stirred for 30 minutes, 4.00 mL of the solution containingmaterial D and isopropanol was added to the beaker gradually whilestirring. After 10 minutes, the suspension started to flocculate. Thebeaker was covered with Parafilm® and left in the dry box overnightundisturbed. Two layers—a clear solvent layer and a dark fluffy layer atthe bottom of the beaker—were formed. The clear supernatant wasseparated, leaving about a 2 mm thick layer. Upon removal from the drybox, the wet Teflon® stir bar was removed from the beaker. As theTeflone stir bar dried. a thick metallic film began to form on it. Therecovered material from the dark fluffy layer, resembling a dark “ink,”contained the encapsulated metal particles and could be handled atambient conditions in a variety of applications.

EXAMPLE 6

Preparation and Application of Isolated Particles

An “ink” of the concentrated, isolated particles of the presentinvention was prepared for use in coating copper pads and as a metalink.

A suspension of tin/lead particles in isopropanol was prepared using arotary reactor equipped with resistance heating sources. The particlesin the suspension were 68 nm in diameter as determined by photoncorrelation spectroscopy from five replicate samples. Metal loading inthe suspension was 2.76 mg/mL of tin and 1.56 mg/mL of lead.

A solution of 65 mL of 25% 1,2,6-hexanetriol in isopropanol was slowlyadded to 325 mL of the suspension while stirring with a magneticstirring bar in an argon-filled dry box. A 0.5% solution oftriethanolamine and malonic acid (5:1 ratio), as an encapsulantmaterial, in isopropanol was added at a rate of 50 μL/s for a totalvolume of 6.5 mL. This addition induced encapsulation of the metalparticles, gradual flocculation, and settling. Eventually, thesupernatant became clear and the wet sediment, constituting the isolatedencapsulated particles, was recovered by decanting the clearsupernatant.

About a third of the sediment containing the encapsulated particles wasremoved from the dry box. A volume of 6.75 mL of absolute methanol,saturated with tin (II) fluoride was added to the sediment and stirred.Excess solvent was allowed to evaporate at ambient condition. Thematerial dried to a crust.

Five drops of glycerol were added to the dried sediment and the sedimentwas mixed with the tip of a spatula. The mixture turned fluid and waswashed with absolute methanol to concentrate it. Excess solvent wasallowed to evaporate until the mixture became nearly dry. A small amountof the material was mixed with triethanolamine/malonic acid (5:1 ratio)until good reflow was achieved. Using an automatic liquid dispenser,dots were deposited on copper coupons, and turned to a bright metallicdeposit when reflowed in an IR oven. Dots placed on pads of a Super Novasurface mount printed circuit board formed flat bright coating withslightly rough metallic deposits. When the pads were coated with thetriethanolamine/malonic acid mixture prior the placement of the dots,the deposits became smooth.

Another portion of the recovered isolated encapsulated particles wasused as a metal ink. The ink was used to write on a glass slide, andmetallic inscription was produced on the glass slide when the ink washeated to 180° C. to drive off the organic material of the ink.

EXAMPLE 7

Application of Isolated Particles

Thick “ink” or paste prepared in the manner described in Example 6 wasused to attach electronic components to a surface mount printed circuitboard. The amount of triethanolamine/malonic acid was adjusted untilreflow tests showed the presence of sufficient amount of the encapsulantmaterial, which functions as a fluxing agent, to attach the electroniccomponents. With an automatic dispenser and paste printing device, dotsor pads were printed on the pads of the board. The electronic componentswere placed with a Quad Pick N Place unit. After IR reflow, allcomponents were attached to the board.

The foregoing description of preferred embodiments of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the invention. Theembodiments were chosen and described in order to explain the principlesof the invention and its practical application to enable one skilled inthe art to utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto, and their equivalents.

What is claimed is:
 1. A method of coating a fiber, comprising the stepof: applying to the fiber discrete ultrafine or fine particles that areat least substantially coated with an encapsulant material, wherein theencapsulant material is at least one compound selected from an amine, anether, a thiol, a sulfide, a hydroxy acid, a sulfonic acid, anorganosilane, a titanate, a zirconate, a zircoaluminate, a sulfate, asulfonate, an ammonium salt, a pyrrole, a furan, a thiophene, animidazole, an oxazole, a thiazole, a pyrazole, a pyrroline, apyrrolidine, a pyridine, a pyrimidine, a purine, a triazole, and atriazine.
 2. The method of claim 1, wherein the encapsulant material isat least one compound selected from triethanol amine, ethylenediamine,oleic acid, malonic acid, hydroxyacetic acid, dimethyl sulfoxide,propylene glycol, hexanetriol, dioxane, diethylene glycol dimethylether, dimethylformamide, 1-(2-cyanoethyl)pyrrole,3-(2-furyl)acrylonitrile, 3-thiophenemalonic acid,mercaptobenzimidazole, 2-mercaptobenzoxazole, 6-aminobenzothiazole,3-(2-aminoethyl)pyrazole, 1-pyrrolidinebutyronitrile, 3-pyridineacrylicacid, 4,6-dihydroxypyrimidine, 6-mercaptopurine, 1-chlorobenzotriazole,2,4,6-triallyloxy-1,3,5-triazine, undecanethiol, diundecyl disulfide,trimethylethoxysilane, isopropyltriisostearoyltitanate,neoalkoxytrisneodecanoylzirconate, sodium stearate, sodium cetylsulfate, sodium diisopropylnapthalene sulfonate, andcetyltrimethylammonium bromide, and derivatives thereof.
 3. The methodof claim 1, wherein the particles comprise at least one metal having anatomic number ranging from 21 to 32, 39 to 50 or 72 to
 82. 4. The methodof claim 1, wherein the encapsulated particles comprise at least oneelement or compound selected from metal elements, organic or inorganiccompounds capable of forming colloidal suspensions of particles, andsolid non-metal elements capable of forming colloidal suspensions ofparticles.
 5. The method of claim 1, wherein the encapsulant material isin direct contact with the surface of each ultrafine or fine particle.6. A method of coating a fiber, comprising the step of: applying to thefiber discrete ultrafine or fine particles that are at leastsubstantially coated with an encapsulant material, wherein theencapsulant material is at least one compound selected from an amine, anether, a thiol, a sulfide, a carboxylic acid, a hydroxy acid, a sulfonicacid, an organosilane, a titanate, a zirconate, a zircoaluminate, acarboxylate, a sulfate, a sulfonate, an ammonium salt, a pyrrole, afuran, a thiophene, an imidazole, an oxazole, a thiazole, a pyrazole, apyrroline, a pyrrolidine, a pyridine, a pyrimidine, a purine, atriazole, and a triazine; wherein said ultrafine or fine particlescomprise at least one element or compound selected from metal elements,organic or non-oxide inorganic compounds capable of forming colloidalsuspensions of particles, and solid non-metal elements capable offorming colloidal suspensions of particles.
 7. The method of claim 6,wherein the encapsulant material is at least one compound selected fromtriethanol amine, ethylenediamine, oleic acid, malonic acid,hydroxyacetic acid, dimethyl sulfoxide, propylene glycol, hexanetriol,dioxane, diethylene glycol dimethyl ether, dimethylformamide,1-(2-cyanoethyl) pyrrole, 3-(2-furyl) acrylonitrile, 3-thiophenemalonicacid, mercaptobenzimidazole, 2-mercaptobenzoxazole,6-aminobenzothiazole, 3-(2-aminoethyl) pyrazole,1-pyrrolidinebutyronitrile, 3-pyridineacrylic acid,4,6-dihydroxypyrimidine, 6-mercaptopurine, 1-chlorobenzotriazole,2,4,6-triallyloxy-1,3,5-triazine, undecanethiol, diundecyl disulfide,trimethylethoxysilane, isopropyltriisostearoyltitanate,neoalkoxytrisneodecanoylzirconate, sodium stearate, sodium cetylsulfate, sodium diisoprophyinapthalene sulfonate, andcetyltrimethylammonium bromide, and derivatives thereof.
 8. The methodof claim 6, wherein the particles comprise at least one metal having anatomic number ranging from 21 to 32, 39 to 50 or 72 to
 82. 9. The methodof claim 6, wherein the encapsulant material is in direct contact withthe surface of each ultrafine or fine particle.
 10. A method of forminga coating on a substrate, comprising the step of: applying to thesubstrate a composition comprising discrete ultrafine or fine particlesat least substantially coated with an encapsulant material, wherein theencapsulant material is at least one compound selected from an amine, anether, a thiol, a sulfide, a hydroxy acid, a sulfonic acid, anorganosilane, a titanate, a zirconate, a zircoaluminate, a sulfate, asulfonate, an ammonium salt, a pyrrole, a furan, a thiophene, animidazole, an oxazole, a thiazole, a pyrazole, a pyrroline, apyrrolidine, a pyridine, a pyrimidine, a purine, a triazole, and atriazine.
 11. The method of claim 10, wherein the encapsulant materialis at least one compound selected from triethanol amine,ethylenediamine, oleic acid, malonic acid, hydroxyacetic acid, dimethylsulfoxide, propylene glycol, hexanetriol, dioxane, diethylene glycoldimethyl ether, dimethylformamide, 1-(2-cyanoethyl)pyrrole,3-(2-furyl)acrylonitrile, 3-thiophenemalonic acid,mercaptobenzimidazole, 2-mercaptobenzoxazole, 6-aminobenzothiazole,3-(2-aminoethyl)pyrazole, 1-pyrrolidinebutyronitrile, 3-pyridineacrylicacid, 4,6-dihydroxypyrimidine, 6-mercaptopurine, 1-chlorobenzotriazole,2,4,6-triallyloxy-1,3,5-triazine, undecanethiol, diundecyl disulfide,trimethylethoxysilane, isopropyltriisostearoyltitanate,neoalkoxytrisneodecanoylzirconate, sodium stearate, sodium cetylsulfate, sodium diisopropylnapthalene sulfonate, andcetyltrimethylammonium bromide, and derivatives thereof.
 12. A Themethod of claim 10, wherein the particles comprise at least one metalhaving an atomic number ranging from 21 to 32, 39 to 50 or 72 to
 82. 13.The method of claim 10, wherein the encapsulated particles comprise atleast one element or compound selected from metal elements, organic orinorganic compounds capable of forming colloidal suspensions ofparticles, and solid non-metal elements capable of forming colloidalsuspensions of particles.
 14. The method of claim 10, wherein theencapsulant material is in direct contact with the surface of eachultrafine or fine particle.
 15. A method of forming a coating on asubstrate, comprising the step of: applying to the substrate acomposition comprising discrete ultrafine or fine particles at leastsubstantially coated with an encapsulant material, wherein theencapsulant material is at least one compound selected from an amine, anether, a thiol, a sulfide, a carboxylic acid, a hydroxy acid, a sulfonicacid, an organosilane, a titanate, a zirconate, a zircoaluminate, acarboxylate, a sulfate, a sulfonate, an ammonium salt, a pyrrole, afuran, a thiophene, an imidazole, an oxazole, a thiazole, a pyrazole, apyrroline, a pyrrolidine, a pyridine, a pyrimidine, a purine, atriazole, a triazine; wherein said ultrafine or fine particles compriseat least one element or compound selected from metal elements, organicor non-oxide inorganic compounds capable of forming colloidalsuspensions of particles, and solid non-metal elements capable offorming colloidal suspensions of particles.
 16. The method of claim 15,wherein the encapsulant material is at least one compound selected fromtriethanol amine, ethylenediamine, oleic acid, malonic acid,hydroxyacetic acid, dimethyl sulfoxide, propylene glycol, hexanetriol,dioxane, diethylene glycol dimethyl ether, dimethylformamide,1-(2-cyanoethyl) pyrrole, 3-(2-furyl) acrylonitrile, 3-thiophenemalonicacid, mercaptobenzimidazole, 2-(2-furyl) acrylonitrile,3-thiophenemalonic acid, mercaptobenzimidazole, 2-mercaptobenzoxazole,6-aminobenzothiazole, 3-pyidineacrylic acid, 4,6-dihydroxypyrimidine,6-mercaptopurine, 1-chlorobenzotriazole,2,4,6-triallyloxy-1,3,5-triazine, undecanethiol, diundecyl disulfide,trimethylethoxysilane, isopropyltriisostearoyltitanate,neoalkoxytrisneodecanoylzirconate, sodium stearate, sodiumcetylcytrimethylammonium bromide, and derivatives thereof.
 17. Themethod of claim 15, wherein the particles comprise at least one metalhaving an atomic number ranging from 21 to 32, 39 to 50 or 72 to
 82. 18.The method of claim 15, wherein the encapsulant material is in directcontact with the surface of each ultrafine or fine particle.
 19. Amethod of joining metal to a substrate, comprising the steps of:applying to the substrate discrete ultrafine or fine particles at leastsubstantially coated with an encapsulant material, wherein theencapsulant material is at least one compound selected from an amine, anether, a thiol, a sulfide, a carboxylic acid, a hydroxy acid, a sulfonicacid, a polyhydroxy alcohol, an organosilane, a titanate, a zirconate, azircoaluminate, a carboxylate, a sulfate, a sulfonate, an ammonium salt,a pyrrole, a furan, a thiophene an imidazole, an oxazole, a thiazole, apyrazole, a pyrroline, a pyrrolidine, a pyridine, a pyrimidine, apurine, a triazole a triazine, and derivatives thereof; and placing saidmetal to be joined in contact with the discrete ultrafine or fineparticles.
 20. The method of claim 19, wherein the encapsulant materialis at least one compound selected from triethanol amine,ethylenediamine, oleic acid, malonic acid, hydroxyacetic acid, dimethylsulfoxide, propylene glycol, hexanetriol, dioxane, diethylene glycoldimethyl ether, dimethylformamide, 1-(2-cyanoethyl)pyrrole,3-(2-furyl)acrylonitrile, 3-thiophenemalonic acid,mercaptobenzimidazole, 2-mercaptobenzoxazole, 6-aminobenzothiazole,3-(2-aminoethyl)pyrazole, 1-pyrrolidinebutyronitrile, 3-pyridineacrylicacid, 4,6-dihydroxypyrimidine, 6-mercaptopurine, 1-chlorobenzotriazole,2,4,6-triallyloxy-1,3,5-triazine, undecanethiol, diundecyl disulfide,trimethylethoxysilane, isopropyltriisostearoyltitanate,neoalkoxytrisneodecanoylzirconate, sodium stearate, sodium cetylsulfate, sodium diisopropylnapthalene sulfonate, andcetyltrimethylammonium bromide, and derivatives thereof.
 21. The methodof claim 19, wherein the particles comprise at least one metal having anatomic number ranging from 21 to 32, 39 to 50 or 72 to
 82. 22. Themethod of claim 19, wherein the encapsulated particles comprise at leastone element or compound selected from metal elements, organic orinorganic compounds capable of forming colloidal suspensions ofparticles, and solid non-metal elements capable of forming colloidalsuspensions of particles.
 23. The method of claim 19, wherein theencapsulant material is in direct contact with the surface of eachultrafine or fine particle.
 24. A method of joining metal to asubstrate, comprising the steps of applying to the substrate discreteultrafine or fine particles at least substantially coated with anencapsulant material, wherein the encapsulant material is at least onecompound selected from an amine, an ether, a thiol, a sulfide, acarboxylic acid, a hydroxy acid, a sulfonic acid, a polyhydroxy alcohol,an organosilane, a titanate, a zirconate, a zircoaluminate, acarboxylate, a sulfate, a sulfonate, an ammonium salt, a pyrrole, afuran, a thiophene, an imidazole, an oxazole, a thiazole, a pyrazole, apyrroline, a pyrrolidine, a pyridine, a pyrimidine, a purine, atriazole, a triazine, and derivatives thereof; and placing said metal tobe joined in contact with the discrete ultrafine or fine particles,wherein said ultrafine or fine particles comprise at least one elementor compound selected from metal elements, organic or non-oxide inorganiccompounds capable of forming colloidal suspensions of particles, andsolid non-metal elements capable of forming colloidal suspensions ofparticles.
 25. The method of claim 24, wherein the encapsulant materialis at least one compound selected from triethanol amine,ethylenediamine, oleic acid, malonic acid, hydroxyacetic acid, dimethylsulfoxide, propylene glycol, hexanetriol, dioxane, diethylene glycoldimethyl ether, dimethylformamide, 1-(2-cyanoethyl) pyrrole, 3-(2-furyl)acrylonitrile, 3-thiophenemalonic acid, mercaptobenzimidazole,2-mercaptobenzoxazole, 6-aminobenzothiazole, 3-(2-aminoethyl) pyrazole,1-pyrrolidinebutyronitrile, 3-pyridineacrylic acid,4,6-dihydroxypyrimidine, 6-mercaptopurine, 1-chlorobenzotriazole,2,4,6-triallyloxy-1,3,5-triazine, undecanethiol, diundecyl disulfide,trimethylethoxysilane, isopropyltriisostearoyltitanate,neoalkoxytrisneodecanoylzirconate, sodium stearate, sodium cetylsulfate, sodium diisoprophylnapthalene sulfonate, andcetyltrimethylammonium bromide, and derivatives thereof.
 26. The methodof claim 24, wherein the particles comprise at least one metal having anatomic number ranging from 21 to 32, 39 to 50 or 72 to
 82. 27. Themethod of claim 24, wherein the encapsulant material is in directcontact with the surface of each ultrafine or fine particle.